Building new system starting with power amp. What would you choose ?

Levinson ML-2 is a great idea. Can it still be serviced ? I read about it but never heard it.
Gryphon Diablo is yes, basically a power amp with passive preamp. However, I would try to find used Gryphon Class A power amp. instead of it first.

Sanders sound Magtech mono blocs. 
 Any warm speaker. (86-90 db 1w/1m)
 CJ  ET5 SE. 
 Rotel 1572 CD player.Audioquest cables.

 8 ga speaker cables.

 Bottle of Bushmills 21yr single malt Irish whisky!
Can of Copenhagen long cut.

 Leave me alone!!!!

Oh, I missed the point, what would WE choose? What would I choose?. 

I thought you meant, you had already see an amp you 'must' have.

15k budget, that's more than I would spend, I have efficient speakers, so I have the advantage of staying in 25, 35-45 wpc range which are more affordable.

I researched, chose my Cayin, love it, it never occurs to me to consider another. That left me with 12K to spend on other stuff. Well, I would like external bias adjusters and meters.

Based upon childhood memories (Leak)...

A properly refurbished Leak ST 20 (might need a quality repop PT in the redo) paired with contemporary easy to drive speakers.

Also intrigued by the less expensive David Berning/LTA offerings but have only briefly listened to a couple of his amps (the last being maybe 15 years ago and the other way before that).

I recently posted about a Roger Modjeski EL84 based power amp that I also find special in that it's sound was different, but also incredibly pleasing instead of odd.

It didn't seem to to compress with busy source material and instead remained 3D/open (and this from 2 EL84's per channel).

Not up on new stuff (as you can imagine by my posted rig).

Go to your favorite audio dealer(s) and listen.  Learn.  Observe.  Make a judgement.

Just keep in mind that tube amps require care and feeding that solid state amps do not.  Depending of the rest of your system, a very good solid state amp will give you as much satisfaction as a tube amp without the tube amp hassle.